Each year approximately 300 million used tires are discarded. Many of these used tires are put into landfills or, all too often, are disposed of illegally. Such disposal of scrap tires in landfills is becoming increasingly undesirable as significant environmental and social problems are associated with such activity. The availability of landfill space is diminishing, and there has been a national trend toward more stringent regulatory requirements on landfills. Hence, a considerable amount of attention has been devoted recently toward finding alternative uses for and methods of reclaiming scrap tires.
Some research and commercial efforts have been directed toward the development of new uses for old tires. Unprocessed used tires have been used in playgrounds, flower planters, and shoe soles, and tire pieces have been used as gaskets, shims, dock bumpers and shock absorbers. Processed wasted tires are used as fuel in paper plants and cement kilns and as filler in road construction. Paving materials made from a combination of crumb rubber and asphalt may last up to three times as long as customary paving materials. However, because of the high costs associated with the use of scrap tires for roads, this approach has not gained wide acceptance. Studies continue to explore this use of scrap tires in addition to the somewhat more conventional use of tires as crash barriers and impact absorbers around highway and bridge abutments. However, these new applications for used tires or their constituents consume only a minor portion of the annual accumulation of scrap tires.
Another approach to tire recycling is the generation of solid carbonous residues inside a screw reactor system. Here, “carbonous” represents a state-of-the-art term employed in the field of asphalt materials to indicate largely-carbon-containing molecular structures or particulate entities. Systems and methods for producing carbonous residues from recycled tires are known in the art. For example, U.S. Pat. No. 5,389,691 to Cha, et al. discloses such a system and method. It is incorporated herein by reference in its entirety to the extent it is not inconsistent with the present disclosure. There are some differences between the present invention and U.S. Pat. No. 5,389,691, hereinafter referred to as '691, that will be evident from the following description.
The carbonous residues may have a variety of uses, including being used as an additive in certain types of concrete. However, the carbonous residues produced by the aforementioned processes have a limited and specific application range. For example, they are not suitable for various environmental applications, due to low surface area, small pore size and chemical composition. Therefore, what is desired is a carbonous residue and process for making the residue from recycled tires that is suitable for environmental applications.